This invention relates to a diesel engine control system and particularly to a closed loop air/fuel ratio control system for a diesel engine.
It is generally known that emissions of nitrogen oxides from diesel engines can be reduced by recirculating a portion of exhaust gases to the intake of the engine. Current diesel engine exhaust gas recirculation controls provide for control of the amount of exhaust gas recirculation (EGR) based on an open loop schedule. Since the control is open loop, these systems do not provide for active correction for variability due to production tolerances, wear, dirty air filters, fuel, ambient conditions, etc. so that the actual amounts of exhaust gases recirculated may vary from the intended amount.
It is also generally known that the smoke and particulate emissions from a diesel engine may be lessened by preventing the air/fuel ratio from becoming too rich. Typically, this rich limit is imposed by mapping the fuel delivery which is preset prior to delivery of the engine. Thereafter, no active corrections are made for pump wear, fuel viscosity, dirty air filters, ambient changes, etc. so that the actual air/fuel ratio limit may vary from the intended limit.